Employee Benefit Plans - Components of Net Period Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 17	$ 71	$ 52	$ 255
Interest cost	726	692	2,180	2,063
Expected return on plan assets	(751)	(889)	(2,257)	(2,686)
Amortization of net loss	517	614	1,551	1,592
Amortization of prior service cost	8	4	25	23
Net pension benefit cost	517	492	1,551	1,247
Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	5	5	17	15
Expected return on plan assets	0	0	0	0
Amortization of net loss	(1)	0	(3)	0
Amortization of prior service cost	0	0	0	0
Net pension benefit cost	4	5	14	15
Retirement Income Plan | Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	8	0	23
Interest cost	397	354	1,192	1,063
Expected return on plan assets	(440)	(512)	(1,320)	(1,535)
Amortization of net loss	377	311	1,132	933
Amortization of prior service cost	0	0	0	0
Net pension benefit cost	334	161	1,004	484
National Service-Related Pension Plan | Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	20	0	59
Interest cost	312	300	934	899
Expected return on plan assets	(294)	(342)	(882)	(1,027)
Amortization of net loss	141	179	422	536
Amortization of prior service cost	0	0	0	0
Net pension benefit cost	159	157	474	467
Superannuation | Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	17	43	52	173
Interest cost	12	33	37	86
Expected return on plan assets	(17)	(35)	(55)	(124)
Amortization of net loss	0	124	0	123
Amortization of prior service cost	8	4	25	23
Net pension benefit cost	$ 20	$ 169	$ 59	$ 281